Stem Cells for Sex, Smell Discovered in Mice

by Wynne Parry | July 30, 2010 04:59am ET

The cellular origin of smell, sex and self-recognition has
been discovered in a study of mice.

The new research shows that during embryonic development, a
set of cells that line what will become the nose, give rise to three types of
neurons that carry signals making these three functions possible.

"These cell types are key for the survival of an
organism," said researcher Anthony-Samuel LaMantia, director of the George
Washington Institute for Neuroscience."You can't get more essential than that." LaMantia conducted the research while at the
University of North Carolina, Chapel Hill.

Nasal neurons

LaMantia's team isolated the stem cells from mouse embryos
about halfway through their 20-day gestation. After 20 hours, cells they took
from the sides of the lining of the nasal cavity (called the olfactory
epithelium) produced only more of themselves — a key feature of stem cells, he
said.

The results also showed the nasal stem cells went on to
become the three types of nerve cells: olfactory (responsible for our sense of smell),
pheromonal (linked to the ability to sense pheromones)
and gonadotropin (linked to reproduction).

Once formed, the neurons associated with reproduction,
gonadotropin releasing hormone neurons, leave the nasal tissue and migrate to
the brain's hypothalamus, a region of the brain that controls many body
functions. These neurons are responsible for the release of two hormones: luteinizing
hormone, which triggers ovulation in women and testosterone production for
males; and follicle-stimulating hormone, which regulates puberty
and reproductive processes in the body.

While the sex neurons don't regenerate, the olfactory and pheromonal
neurons (called vomeronasal receptor neurons) are unique in that they can
regenerate. Humans have nearly lost our ability to sense the chemical signals, pheromones,
researchers speculate.

Autism, schizophrenia
and other diseases

The results could have important medical implications,
particularly for the so-called olfactory receptor neurons. These nerve cells
hide out in the nose, detecting chemical signals, which they communicate to the
brain via long stems called axons.

"Over the course of a lifetime, it turns out in most
parts of the nervous system, the neurons you start with when you are born are
the neurons you end up with. If you lose them, you don't replace them," he
said. "Except for in the nose."

There is evidence of the limited addition of new cells in
the hippocampus,
but otherwise, the nose is unique, and olfactory neurons' ability to regenerate
could aid in the study of diseases, like autism and schizophrenia, where the
sense of smell is altered, he said.

Because these neurons could survive a biopsy, they could
potentially be used to study the progression of these diseases. And since some,
like autism and schizophrenia, are diagnosed only by observation, olfactory
neurons might yield diagnostic tools, he said.

Wynne Parry

Wynne was a reporter at The Stamford Advocate. She has interned at Discover magazine and has freelanced for The New York Times and Scientific American's web site. She has a masters in journalism from Columbia University and a bachelor's degree in biology from the University of Utah.